The present invention relates to a variable crown sleeve roll and, more particularly, to an improved sleeve roll in which a chamber is defined between the outer peripheral surface of the arbor and the inner peripheral surface of the sleeve to permit control of the amount of expansion of the outer diameter of the roll by supplying a pressurized fluid to said chamber.
In the ensuing description, the amount of the diametrical expansion of the outer diameter of the roll is represented by the term "crown", the rolled steel plate is referred to as "strip", and the effect for making the thickness of the strip uniform and relieving the sharp local variation in the rolling pressure is referred to as the "softening effect".
In a rolling operation such as cold rolling, as generally known, since the rolls are subject to an extremely large rolling load which is applied to the rolls through bearings at the opposite ends thereof, the axes of the upper and the lower rolls are curved outwardly at the central portions of their lengths when a strip is held between the rolls, with the result that the rolled strip is thicker in the central region, in the duration of its width, than in other regions. In order to compensate for the curvature of the axes of the rolls and to make the strip thickness uniform, it is conventional to make the rolls by a method generally referred to as "crowning" in which each of the rolls is formed in a barrel-shape by progressively increasing the outer diameter of the roll from the opposite axial ends toward the central portion. The roll crown according to the conventional crowning method, has, however, a serious disadvantage in that the amount of the roll crown once determined in accordance with a certain rolling condition is not adjustable in response to changes in the rolling conditions or in the width of the strip being rolled.
This disadvantage has been overcome by a sleeve roll disclosed in Japanese Patent Application No. 18575/75 (Japanese Published Application No. 92770/76), in which the amount of the crown is variable and which has a softening effect. In this roll, a sleeve has the inner peripheral surface fitted on the peripheral surface of, an arbor and sealing means and securing means are provided at opposite ends of the fitting surface, step portions are machined in the inner peripheral surface of the sleeve or the outer peripheral of the arbor or both in the central portions of the fitting surfaces to define a sealed cylindrical chamber therebetween, and a fluid passage comprising a bore extending from an end face of the arbor therethrough and bores branching from said bore and extending to said sealed cylindrical chamber are provided.
The first characteristic of the operational effect of the roll disclosed by said Japanese Patent Application No. 18575/75 is that the sealed cylindrical chamber formed with the stepped portion thereabout substantially parallel to the fitting surfaces (in other words, the height of the stepped portion is constant with respect to the axial direction of the roll) can be supplied with a pressurized fluid, preferably oil, from outside through a rotary connection connected to the fluid passage to thereby elastically deform the outer peripheral surface of the sleeve so as to control the amount of the crown by adjusting the pressure of said fluid.
The second characteristic of the operational effect of said roll is that when some flaw such as a ridge-like local projection exists on the surface of the strip (heretofore such a projection was crushed flat by pressure and caused ridge buckles in the strip due to a difference extending in the rolling direction in the uneven region) the surface of the roll is depressed at the position corresponding to the projection on the strip because of the softening effect to relieve the sharp local variation of the linear pressure between the upper and the lower rolls with the strip therebetween to thereby roll the strip uniformly flat.
The roll disclosed in said Japanese Patent Application No. 18575/75 has the curvature of the crown substantially flat in a relatively wide range from the center of the width of the roll toward the opposite ends thereof.
After extensive research on the relationship between the crown of the roll and the shape of the strip produced thereby, the inventors have found that for a roll to produce a strip of a uniform thickness it is of a vital importance that the roll crown have a curvature in which the size of the substantially flat portion in the center of the width of the roll is reduced.
Japanese Patent Application No. 133312/75 (Japanese Published Application No. 57065/77) discloses an improved sleeve roll the shape of which is based on the above-described finding in which the sleeve has a progressively decreasing thickness from the opposite ends toward the center thereof or, in other words, the radial dimension of the sealed chamber progressively increases from the opposite ends toward the center thereof.
Further research by the inventors has revealed that a strip cannot be rolled into a satisfactory shape unless the sleeve thickness, the sleeve thickness taper angle, and the internal pressure receiving length are designed within certain limitations in accordance with the rolling conditions such as the cross sectional shape of the slab, the width of the strip, and the rolling load.
Accordingly, an object of the present invention is to provide a sleeve roll capable of providing the optimum control of the roll crown and producing the optimum softening effect in accordance with the rolling conditions.